The present invention is directed to write driving apparatuses and methods associated with memory devices. In particular, the present invention is directed to a write driver apparatus that is constructed to accommodate configuring according to various predetermined operational criteria, and directed to a method for effecting such configuring.
During the writing of information to a storage medium such as a magnetic disk in an electromagnetic storage device a write current (IW) is supplied, generally by a preamplifier apparatus, to a write head that is situated adjacent to the magnetic disk. The polarity of write current IW passing through the write head (i.e., the direction of travel of the write current) influences magnetic properties in the magnetic disk and effects storage of digital information in the disk. In addition to a steady-state write current IW, it is desirable to have additional current available during the transition toward steady state IW to assure a successful write operation. Such extra current above steady state write current IW is called boost current IBST and is preferably supplied only during periods in which write current IW is transitioning from one current level, or value, to another current level. Applying boost current IBST usually results in write current IW momentarily going beyond its steady state current level, a condition known as overshoot.
The load seen by a preamplifier device associated with a write device is a complex load (representing the write head and interconnections between the write head and the preamplifier) so that some ringing is typically present as write current returns to its steady state level IW from an overshoot condition. One method of reducing ringing is to introduce some damping at the input to the writer head, such as by introducing an output resistance ROUT at the locus to which the writer head is connected. Output resistance ROUT can be installed either connected in series or in parallel with the writer load.
Different manufacturers of electromagnetic storage products require different operational characteristics for write apparatuses they employ in their respective products. A manufacturer of component write apparatuses (commonly and preferably embodied in assemblies known as head stack assemblies) for use by product manufacturers needs to match the requisite parametric requirements of various customer-producers. In meeting the various operational parametric requirements there are opposite tendencies among various parameters that must be accommodated.
For example, a larger value for output resistance ROUT is best when one seeks to employ a lower write current IW. In such conditions, overshoot is easily attained because of the lower value of write current IW. There is no need for a large boost current IBST In contrast, a lesser output resistance ROUT and a larger boost current IBST are best when one uses a higher value for write current IW. Larger boost current IBST is necessary as its value scales up with IW to provide a desired IBST/IW ratio at a higher write current IW setting. Output resistance ROUT may be reduced to minimize loss of voltage headroom (i.e., “running into the upper rail”; approaching the upper supply voltage level), since loss of voltage headroom causes reduction of overshoot. Thus, the requirements for boost current IBST and output resistance ROUT urge parameters ROUT, IBST in opposite directions to seek to achieve a particular operating value for write current IW: lower write current IW urges higher output resistance ROUT and lower boost current IBST, higher write current IW urges lower output resistance ROUT and higher boost current IBST. Some prior art write apparatuses provided for programmable boost current IBST. Some prior art write apparatuses provided for programmable output resistance ROUT. However, programming of the respective parameters boost current IBST and output resistance ROUT was accomplished using separate control units, such as separate digital-to-analog converter (DAC) units.
The inventor had observed that complete control of the parameters output resistance ROUT and boost current IBST does not need to be effected to configure a write apparatus for optimal performance using a variety of values of write current IW. That is, one need only control situations in which one of parameters ROUT, IBST is increased while the other of parameters ROUT, IBST is decreased, or vice versa. No provision needs to be made for increasing or decreasing both of parameters ROUT, IBST together. Programming coverage needs only to address two quadrants (i.e., one quadrant: ROUT increases, IBST decreases or another quadrant: IBST increases, ROUT decreases) of parameter variations. The remaining two quadrants (i.e., one quadrant: ROUT increases, IBST increases or another quadrant: ROUT decreases, IBST decreases) do not contribute to desired performance by a write apparatus. The remaining two quadrants may therefore be ignored. Providing a single control apparatus for affecting selected circuit parameters to configure a write apparatus for desired operational characteristics lowers parts count for the write apparatus while increasing its flexibility to meet varied requirements of customer-producers. Lower parts count yields several advantages, including by way of example and not by way of limitation, occupying less board space, increased reliability (i.e., fewer parts to break down), lesser power consumption and other efficiencies.
If no programmability of parameters was provided or if only one parameter was programmable, manufacturers of prior art write apparatuses had to produce a number of different apparatuses in order to accommodate differing operational parameters for various customer-producers. Having to produce several specially configured products prevents a manufacturer from enjoying some advantages that can be realized by economies of scale attending large volume manufacturing operations.
There is a need for a single write apparatus, such as a head stack assembly providing a preamplifier device and an associated write head, that can be configured to conform to a variety of predetermined operational characteristics, and a method for effecting such configuring.
There is a need for a single control apparatus for affecting selected circuit parameters to configure a write apparatus for desired operational characteristics.